Immunoglobulins M and G (IgM and IgG) were purified from rat serum and secretory IgA from rat colostrum by molecular sieve, ion exchange and affinity chromatography. Purification of IgM was complicated by contamination with a alpha2, macroglobulin. Antisera to these purified immunoglobulins were raised in New Zealand white rabbits. The antisera were rendered monospecific by immunoabsorption of affinity supports. Antisera have been coupled to fluorescein isothiocyanate and alkaline phosphatase. Attempts were made to devise simple repreducible methods for purification of IgG subclasses.